To calculate the exchange current density i0 for the corroding iron electrode, we can use the Butler-Volmer equation. However, we need to first determine the transfer coefficient and the number of electrons transferred n in the reaction. For the Fe2+/Fe redox couple, n = 2 electrons, and is typically assumed to be 0.5.The standard rate constant k0 can be calculated using the following equation:k0 = i0 / n * F * C where F is the Faraday constant 96485 C/mol and C is the concentration of Fe2+ ions 0.1 M .Rearranging the equation to solve for i0:i0 = k0 * n * F * CNow, we can plug in the given values:i0 = 1.2 x 10^-9 cm/s * 2 * 96485 C/mol * 0.1 Mi0 = 2.318 x 10^-5 A/cmSo, the exchange current density for the corroding iron electrode in a 0.1 M solution of Fe2+ ions at 25C is approximately 2.318 x 10^-5 A/cm.